subscribe_url example

public function get_base($element = array())
    {
        if (!($this->get_type() & SIMPLEPIE_TYPE_RSS_SYNDICATION) && !empty($element['xml_base_explicit']) && isset($element['xml_base']))
        {
            return $element['xml_base'];
        }
        elseif ($this->get_link() !== null)
        {
            return $this->get_link();
        }

        return $this->subscribe_url();
    }

    /** * Sanitize feed data * * @access private * @see SimplePie_Sanitize::sanitize() * @param string $data Data to sanitize * @param int $type One of the SIMPLEPIE_CONSTRUCT_* constants * @param string $base Base URL to resolve URLs against * @return string Sanitized data */